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Unfortunately, there's no easy answer to this question. It depends on what your climate is like and how much sun your plants are get. In my area, tomato plants might need up to a gallon of water per day in the peak of summer, but that would be too much in a place where the heat only reaches 75 degrees. Tomatoes don't like to dry out but they also don't like to stay wet. They can get wilt diseases easily when the soil is too damp. That said, you'll have to experiment. Start by making sure your pot is large enough, because a small pot will dry out too soon. Give your plant a good soak in the morning and check it the next day. If the soil still feels damp, leave the plant alone. Don't water again until the soil is dried out 3" below the surface. Continue this cycle until you get a good feel for how long it takes your plant to absorb water. Good luck!